Downstream effects of a dammed reservoir on streamflow and vegetation in East Texas

Downstream effects of Sam Rayburn Dam, Texas on streamflow and vegetation communities on the Angelina River were compared with a relatively similar site, only 20 km apart in an east-west direction, on the Neches River. Annual streamflow discharge was not affected by the impoundment, but monthly stream flows were higher in the summer, duration of high flows was lower and spring peak flows and flood conditions were alsb reduced due to reservoir operation and management. Rainfall had no effect on the alteration of streamflow. Species diversity, richness and evenness are increased below the dam. Species composition was altered to retain more mesic hardwood saplings and reduce wetland herbaceous plants. Oak growth and stand area were also reduced due to less sediment deposition, lower soil moisture content and increased plant competition. The dam made the downstream area a more diverse and stable ecosystem.